The experiments described in this proposal seek to answer two empirical questions that are important to any memory retrieval theory. Experiment 1 is designed to allow direct comparisons between decay rates for priming, repetition and recency. Subjects will be presented with a list of paired associates and then tested with single words, one at a time, and will be required to respond "yes" if the test work was in the study list and "no" if not. In the test list, if one member of a pair is immediately preceded by the other member of the pair, then there is a 150 msec priming effect in response latency. The priming effect will be observed at several different lags along with repetition of test words as a function of lag and recency (accuracy and latency as a function of study position). If priming, repetition and recency show different decay rates, then it will be necessary to postulate different mechanisms for the three kinds of activation. Experiment 2 is designed to investigate the time course of retrieval of semantic information. The main aim is to arrange the semantic question so that similarity information suggests a "yes" response, whereas superordinate information suggests a "no" response by using, for example, questions such as "is a bird a robin?" The response signal method is used to trace out the time course of retrieval. In a typical trial, subjects are presented with the first part of the semantic question ("is a bird a") followed after a short delay by the second part ("robin"). A response signal, presented at a variable time after the second part of the question, is the signal for the subject to respond. A d' analysis may be carried out using a neutral control condition (to supply the "noise" distribution in signal detection terms). The main result expected is that d' as a function of response signal lag will be nonmonotonic, thus suggesting that indeed the similarity and superordinate information are available at different times to the matching mechanism.